Needle thread wiper of sewing machine
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a needle thread wiper for a sewing machine for retaining the needle thread connected to the needle, which is stopped at the top stopping position, and is cut off from the cloth, so as not to slip off from the tip of the needle. 
     2. Description of the Prior Art 
     This type of needle thread wiper for a sewing machine is disclosed, for example, in Japanese Utility Model Publication No. 61-8863. What is disclosed herein comprises, as shown in FIG. 4 herein, a guide 103 having a U-section with its upper end fixed to the side of the arm head of sewing machine 101, and a thread capturing element 104 slidable along the groove 103a of the guide 103. In the portion excluding the lower part of the guide 103, a cover 105 for covering the opening of the groove 103a is provided. The guide 103 is bent approximately in a J-form so that its lower end may approach the needle thread connected to the needle thread passage between the needle 102 stopped at the top position and the cloth (not shown). The bottom surface of the groove 103a forms the guide surface of the thread capturing element 104 communicating with the upper and lower ends of the guide 103. On the other hand, the thread capturing element 104 is formed as a plate extending along the guide surface of the guide groove 103a, and at its front end there is a hook 104a for capturing the needle thread. Meanwhile, the thread capturing element 104 is flexible so as to press the hook 104a to the guide surface of the groove 103a at the bent part of the guide 103. This thread capturing element 104 is engaged with the groove 103a slidably between the action position of crossing the needle thread passage and the waiting position of having the hook 104a pressed to the bottom of the groove 103a. That is, when the hook 104 a at the waiting position is projected along the groove 103a, this hook 104a moves across the needle thread passage. The thread capturing element 104 is usually held at the waiting position by action means not shown herein, and is also allowed to move to the action position after the needle stops at the top position. 
     In such a conventional needle thread wiper for a sewing machine, however, the needle thread captured and pulled by the hook 104a is held between the guide groove 103a and hook 104a. Accordingly, if this holding force is strong, the needle may be broken by the tensioning on the thread when next starting the sewing machine. In particular, in multineedle double chain stitch sewing machines or the like for capturing and pulling plural needles by one hook, this holding force was very strong, and the risk of needle breakage was hence very high. 
     SUMMARY OF THE INVENTION 
     It is hence a primary object of the invention to provide a needle thread wiper for a sewing machine free from needle breakage when sewing is resumed after capturing the needle thread. 
     To achieve the above object, the invention provides a needle thread wiper for a sewing machine which comprises: 
     a guide element fixed on the sewing machine main body and having the front end side formed approximately in a J-form, and 
     a leaf spring slidable on the guide element and having a hook formed at its front end, thereby 
     capturing and pulling the needle thread connected to the needle and cloth by means of the hook of the leaf spring, by sliding the leaf spring along the guide element, the needle thread wiper comprising: 
     a tube-shaped guide element, 
     a hook as a leaf spring which can be inserted from the J-form front end of the guide element into the guide element, and 
     notches formed at the front end portion of the guide element in the positions corresponding to both flat surfaces of the leaf spring, running from the front end of the guide element to the rear end side of the guide element so that the hook of the leaf could be seen through the notches. 
     According to such a construction of the needle thread wiper of the sewing machine, by moving the hook formed at the front end of the leaf spring, the needle thread connected to the needle and cloth can be captured and pulled. The pulled needle thread is introduced into the front end of the guide element together with the hook. The needle thread introduced into the front end of the guide element is guided by the notches formed in the guide element to get into the guide element, and is held in a state of being merely hooked on the hook and guide element. The needle thread held in this state is sequentially let out from the hooking portion, almost without resistance, when sewing is resumed and the needle is lowered. Therefore, breakage of the needle by the pulling force of the needle thread is avoided. Moreover, between the preceding stitch and the next stitch formed, the hook may be placed within the guide element, so that damage to the cloth by the hook is avoided. 
     Thus, in the needle thread wiper for a sewing machine according to the present invention, the leaf spring may be made of a flat wire, and the sliding drive source may be linked to the base part of this leaf spring. Hence, the leaf spring slides smoothly along the guide element. 
     In the needle thread wiper for a sewing machine of another embodiment of the present invention, by the signal generated when the needle of the sewing machine stops at the top position, the sliding drive source moves the leaf spring to the action position where the hook crosses the needle thread connected to the needle and cloth, and then immediately returns this leaf spring to the waiting position where the hook is set in the guide element. Having such a sliding drive source, the needle thread may be automatically set aside at the same time upon end of the sewing operation. 
     These effects are particularly outstanding in the case of multineedle double chain stitch sewing machines. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a perspective view of a cylinder bed sewing machine having a needle thread wiper, 
     FIG. 2A is a partially cut-away perspective view of essential parts showing one stage of the action state of the needle thread wiper, 
     FIG. 2B is a perspective view of essential parts showing another stage of the action state of the needle thread wiper, 
     FIG. 2C is a partially cut-away perspective view of essential parts showing another stage of the action state of the needle thread wiper, 
     FIG. 3 is a perspective view of a guide element, and 
     FIG. 4 is a perspective view of a prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The cylinder bed sewing machine shown in FIG. 1 comprises a needle bar 1 which penetrates through the main body of the sewing machine M. Fixed at the lower end of this needle bar 1 there are three needles 2 arranged in a direction orthogonal to the cloth feed direction (arrow F). The needle bar 1 is supported so as to be movable vertically to the sewing machine main body M, and it moves up and down in cooperation with the main shaft of the sewing machine (not shown). The drive mechanism for moving the needle bar 1 up and down can stop the needles 2 at the top position above the throat plate 3 by known home position stopping means. Corresponding to the needles 2 there is provided an elevatable presser foot 4 for holding the cloth together with the throat plate 3. 
     The sewing machine main body M is furnished with a known thread cutter 5 which cuts the needle thread connected to the needles 2 beneath the throat plate 3. In FIG. 1, however, only the solenoid 5a which is the drive source of this thread cutter 5 installed at the front side of the sewing machine main body M and the lever 5b for transmitting the driving force of the solenoid 5a are shown, and the cutter disposed in the bed 6 and linked to the lever 5b is not shown. 
     The needle thread wiper 7 of the invention is installed at the front side of the arm head A of the sewing machine main body M. This needle thread wiper 7 comprises a guide element 7a, a leaf spring 7b, and an air cylinder 7c. 
     The guide element 7a is in a tube form, of which the lower end side is bent in a J-form and is opened. As shown in FIGS. 2A to 2C, the upper end side of the guide element 7a is fixed to a bracket 8 mounted on the arm head A. The open lower end of the guide element 7a is positioned at a confronting position between the front ends of the needles 2 stopped at the top position above the throat plate 3 and the presser foot 4. As clearly shown in FIG. 3, at the lower end of the guide element 7a bent in a J-form, notches 7aa running from the lower end toward the upper end are formed in the upper and lower surfaces corresponding to both flat surfaces of the leaf spring 7b inserted therein. By the existence of the notches 7aa, the end of the guide element 7a is bifurcated. 
     The leaf spring 7b is a flat wire rod slidably inserted into the guide element 7a. A hook 7ba is formed at the front end of this leaf spring 7b. Meanwhile, as shown in FIG. 1, the base part of the leaf spring 7b is projected from the upper end of the guide element 7a, and it is here linked with the piston rod 7ca of the air cylinder 7c. The hook 7ba is formed in a shape so as to be able to be completely retracted from the lower end opening of the guide element 7a. The leaf spring 7b is slidably supported on the guide element 7a. Or, as shown in FIG. 2A; in the state where the needle threads T are continuously extended between the lower end of the needles 2 stopped at the top position and the cloth (not shown), when the leaf spring 7b slides in the direction of projecting from the lower end of the guide element 7a, the hook 7ba crosses the needle threads T. Afterwards, the hood 7ba hooks the needle threads T so that they can be gathered at the lower end side of the guide element 7a when the hook 7ba slides back to the base part through the guide element 7a. 
     The air cylinder 7c serves as the drive source for sliding the leaf spring 7b. The air cylinder 7c has its cylinder mainbody 7cb fixed at the front side of the arm head A, and the leaf spring 7b linked to the piston rod 7ca is held usually in a state that the hook 7ba is withdrawn in the guide element 7a. When the piston rod 7ca is projected by sending air into the cylinder main body 7cb of this air cylinder 7c, the leaf spring 7b slides along the guide element 7a, so that the hook 7ba at the front end of leaf spring 7b is projected from the front end of the guide element 7a. 
     Besides, as shown in FIG. 1, in front of the needles 2, an eye guard 9 attached to the sewing machine main body M is installed to protect the operator from broken and scattered needles. 
     The operation of the needle thread wiper constructed as noted above in a cylinder bed sewing machine is described below. 
     First, as stated above, usually when forming stitches, this needle thread wiper 7 is held in a state where the hook 7ba of the leaf spring 7b is withdrawn in the guide element 7a by means of the air cylinder 7c. 
     Next, upon completion of forming a stitch, when the needles 2 stop at the top position, a signal is received and air is sent into the cylinder main body 7cb of the air cylinder 7c. As a result, the piston rod 7ca is extended, and the leaf spring 7b slides along the guide element 7a, so that the hook 7ba of the leaf spring 7b is also extended while entangling the needle threads T between the lower end of the needles 2 . . . and the presser foot 4. 
     In this way, as showing FIG. 2A, the hook 7ba extends to the predetermined position, that is, in the case of the illustrated embodiment, to the position of crossing the needle thread T engaged with the needles 2 at the remotest position from the lower end of the guide element 7a. When the hook 7ba reaches this specified position, supply of air into the cylinder main body 7cb is stopped, and then air is sucked from this cylinder main body 7c. As a consequence, the leaf spring 7b is retracted to the air cylinder 7c side, and the hook 7ba once projecting from the guide element 7a is drawn again into the guide element 7a. Along with this withdrawal, as shown in FIG. 2B, the hook 7ba captures the three needle threads T, and pulls them to the front end side of the guide elements 7a. Meanwhile the towed needle threads T are simultaneously cut off and separated from the cloth by the thread cutter 5 beneath the throat plate 3. 
     By continuing to suck air from the cylinder main body 7cb even after the needle threads T are separated from the cloth, the hook 7ba is drawn into the guide element 7a. Along with this, the needle threads T are led into the guide element 7a while being guided along the notches 7aa formed at the front end of the guide element 7a as shown in FIG. 2C. In this way, the needle threads T cut off from the cloth are hooked between the hook 7ba and the guide element 7a, and are held so as not to slip out from the front end of the guide element 7a. 
     Next, to form the next stitch in this state, the needles 2 are lowered, and at this time, since the needle threads T are merely hooked between the hook 7ba and the guide element 7a, the needle threads T are sequentially let out from the hooked portions. Therefore, when lowering the needles 2, the needles 2 . . . are not pulled by the needle threads T, and breakage of the needles 2 . . . upon starting of the formation of the next stitch is prevented. Besides, since the hook 7ba remains within the front end of the guide element 7a before start of the next stitch, damage to the cloth by hooking is avoided. 
     The foregoing embodiment relates to a three-needle sewing machine, but the invention may be applied, needless to say, regardless of the number of needles of the sewing machine. Yet the mechanism for sliding the leaf spring is not limited to the mechanism of using an air cylinder as disclosed in the embodiment, but other mechanism using solenoid or other driving means may be also employed as well.